The present invention relates to devices, commonly referred to as spiders, which engage, hold and support drill pipe or tubing in order to prevent the pipe or tubing from exerting a downward force in the well bore.
Spiders are important in well drilling and servicing operations because they hold the drill pipe so that the weight of the pipe does not exert a downward force into the well. In some cases, the spider may be inverted so as to hold the pipe against upward movement.
An essential feature of a spider is a mechanical means for exerting lateral pressure against the pipe in order to hold its vertical position. Typically, this lateral or radial pressure is generated by a bowl with an opening extending through it in the shape of a conical or pyramidal frustum. The smaller end of the opening is at the lower end of the spider. Slips which engage the bowl surface translate vertical motion of the pipe into a reactive lateral force to squeeze the pipe between the slips.
Hydraulic work-over, or snubbing, services for oil wells are increasingly favoured, having the advantage of eliminating the need to kill the well. In a snubbing operation, it is necessary to use two spiders where one is inverted to grip the pipe and prevent it from moving in either direction. Typically, it is necessary to use four spiders, two of which are inverted. The spiders conventionally used in snubbing operations include slips which pivot into and out of their pipe-engaging position. An example is found is U.S. Pat. No. 4,715,456. Because of the configuration of these spiders, all four spiders cannot be stacked on top of each other. They must be split into two pairs, with a weight-bearing element between them. It would be preferable to eliminate this wasted space to allow the spider configuration to be more compact.
Spiders are known to freeze or otherwise lock up in use. When this occurs, it is typically necessary to cut the spider open to disengage the slips. Also, it is sometimes necessary to pass a larger element of the drill pipe through the spider such as a drill collar or a dog nut which may be larger than the slip opening of prior art spiders will allow. In these cases, it would be preferable to provide a means for disengaging the spider without destroying the spider and perhaps ensuring that the spider may be reused.
The present invention is directed to an improved spider which is compact and robust in construction to allow its use in a limited space. The spider of the present invention may be stacked and bear a full load in a stacked configuration. The spider may be non-destructively opened up in use to disengage it from the drill pipe where necessary.
Accordingly, in one aspect of the invention, the invention comprises an apparatus for engaging, holding and supporting drill pipe or tubing comprising:
(a) a rigid support frame comprising a plurality of support posts each having a lower end and an upper end, a lower support ring engaging the lower end of each support post and an upper support ring engaging the upper end of each support post, wherein said support frame defines a central bore;
(b) a pyramidal frustum comprising a plurality of inclined planes rigidly attached to the support frame and lining the central bore;
(c) a plurality of slips moveable along the inclined planes, each slip interlocking with an inclined plane in a tongue-and-groove or dovetail manner and having a substantially vertical pipe-engaging surface;
(d) means for moving the slips;
wherein the pyramidal frustum and the range of travel of the slips extends substantially the entire length of the support frame between the upper and lower support rings and wherein the pipe-engaging surfaces define a cylindrical opening the diameter of which changes as the slips move along their range of travel.
In a preferred embodiment, each of the upper and lower support rings is comprised of two hemispherical halves which are joined together in a hinged manner such that the rings may be opened or closed. Preferably, the slip moving means comprises two hydraulic cylinders each with a mechanical linkage wherein one cylinder simultaneously moves a first pair of adjacent slips and a second cylinder moves a second pair of adjacent slips. More preferably, movement of the first pair of slips is synchronized with movement of the second pair of slips by means of a horizontal timing bar which slidingly engages a slip of the first pair and an adjacent slip of the second pair.
In a preferred embodiment, the apparatus further comprises a travel limiting block associated with the upper support ring which is moveable between a first position where it does not contact the slip moving means and a second position where it does contact the slip moving means, thereby limiting the upward travel of the slips. The travel limiting block is pivotably attached to the upper support ring and pivots between its first and second position.